diff --git a/NOTES b/NOTES
index 34f9e78..fdbf483 100644
--- a/NOTES
+++ b/NOTES
@@ -1,15 +1,15 @@
 Unite PDFs:
 
-	pdfunite IMG* union.pdf
+	pdfunite $(ls *.pdf | sort -n) union.pdf
 
 
 Rotate 90 degress clockwise:
-	
+
 	pdftk union.pdf cat 1-endeast output 1.pdf
 
 
 Split vertically (use -x for horizontal split):
-	
+
 	mutool poster -y 2 1.pdf
 
 
@@ -19,6 +19,15 @@ Split into separate files, one page per file:
 
 
 Check Djvu metadata:
-	
+
 	djvused -e print-meta book.djvu
 
+
+OCR:
+
+	To see list of languages:
+		tesseract --list-langs
+
+	To perform OCR (overwrites existing OCR layer):
+		ocrmypdf -l rus+eng+fra --redo-ocr --tesseract-timeout 3600 --tesseract-non-ocr-timeout 3600 -O 0 input.pdf output.pdf
+